Page 103 - Introduction to chemical reaction engineering and kinetics

4.5 Problems for Chapter 4 85

(a) Write the chemical equation representing the stoichiometry of the reaction.
(b) Can the course of the reaction be followed by measuring (total) pressure rather than by
the method described above? Explain.
(c) Determine the form of the rate law and the value of the rate constant (in units of L, mol,
s) at 323.1 K, with respect to NO*.
(d) From the following values of the rate constant, with respect to NO2 (units of kPa, min),
given by Czarnowski, determine values of the Arrhenius parameters, and specify the units
of each:
T/K 303.0 323.1 343.1 362.2
lo6 kp (units of kPa, min) 4.4 10.6 20.7 39.8
4-17 A La(Cr, Ni) 0, catalyst was tested for the cleanup of residual hydrocarbons in combustion
streams by measuring the rate of methane oxidation in a differential laboratory flow reactor
containing a sample of the catalyst. The following conversions were measured as a function
of temperature with a fixed initial molar flow rate of methane. The inlet pressure was 1 bar
and the methane mole fraction was 0.25. (Note that the conversions are small, so that the data
approximately represent initial rates.) The rate law for methane oxidation is first-order with
respect to methane concentration.

TPC 250 300 350 400 450
% conversion 0.11 0.26 0.58 1.13 2.3

(a) Explain why initial methane molar concentrations are not constant for the different runs.
(b) Calculate k (s-l) and kb (mol s-l L-’ bar-‘) for each temperature, given that the void
volume in the bed was 0.5 cm3 and the methane molar flow rate into the reactor was 1
mm01 min- l.
(c) Show whether these data obey the Arrhenius rate expression for both k and kb data. What
are the values of EA and Eip? (Indicate the units.)
(d) Explain why, if one of the Arrhenius plots of either k or kb is linear, the other deviates
from linearity. Is this effect significant for these data? Explain.
Comment on the relative magnitudes of
(e) Calculate the pre-exponential factors A and A6,.
v
A and A; as temperature approaches infinity.
7O-v
0 4-18 The Ontario dairy board posted the following times for keeping milk without spoilage. should
(f) How would you determine if factors involving the reaction products (CO2
and H20)
be included in the rate expression?
T/Y 1 Safe storage time before spoilage
0 30 days
3 14 days
15 2 days
22 16 hours
30 3 hours

(a) Does the spoilage of milk follow the Arrhenius relation? Assume spoilage represents a
given “fractional conversion” of the milk. Construct an Arrhenius plot of the data.
0 4-19 The reactions of the ground-state oxygen atom O(3P) with symmetric aliphatic ethers in the gas
(b) What value of activation energy (EA) characterizes this process? (State the units.)
v
7O-v
phase were investigated by Liu et al. (1990) using the flash photolysis resonance fluorescence
technique. These reactions were found to be first-order with respect to each reactant. The rate
constants for three ethers at several temperatures are as follows: